1. Field of the Invention
The present invention relates in general to a vitrified bond tool, and more particularly to such a vitrified bond tool including super abrasive grains and used as a dressing tool for dressing a polishing tool such as a polishing pad which is used for a chemical mechanical polishing of a semiconductor wafer.
2. Discussion of the Related Art
In a process of manufacturing a semiconductor, there is commonly practiced a chemical mechanical polishing (herein after referred to as xe2x80x9cCMPxe2x80x9d) operation. In recent years, since a larger number of sheets of wafers are laminated with a larger scale of integration of electronic circuit, CMP operation is widely practiced for flattening surfaces of the wafers. In CMP operation, a polishing pad and a semiconductor wafer are rotated relative to each other, with application of a polishing fluid including fine abrasive grains to the polishing pad, for polishing the semiconductor wafer. In CMP operation for a semiconductor wafer, a high degree of flatness in the polished surface of the wafer is required by polishing a considerably small amount of the surface of the wafer. For satisfying this requirement, the polishing pad has to be dressed very frequently. The polishing pad has been conventionally dressed by using an electro-deposited diamond tool, which includes a base metal made of stainless or other metallic material, and diamond abrasive grains bonded to the base metal with Ni metal (electro-deposition bond).
JP-A-10-71559 discloses a dresser for dressing a polishing pad used for polishing a semiconductor wafer. This dresser includes a base metal and a diamond thin film. The to base metal has, in its working surface, a multiplicity of protrusions formed by using a wire-EDM (electro-discharge machining) or a metallic mold. The diamond thin film is formed on the working surface of the base metal by a vapor phase synthetic method.
JP-A-10-193266 discloses a method of a vitrified bond tool, which was proposed by the present inventors. This method is characterized by including the step of positioning a screen having a predetermined printing pattern, on a support body; the step of applying a paste including abrasive grains and vitrified bond which are dispersed in the paste, onto the support body through the screen; and the step of sintering the applied paste.
However, the operation for dressing the polishing pad with the electro-deposited diamond tool, in which the diamond abrasive grains are bonded to the base metal by Ni metal as an electro-deposition bond, suffers from elution of Ni metal into the polishing fluid whereby the workpiece is contaminated by Ni metal, particularly, where the polishing fluid is a strong-acid fluid. Further, the electro-deposited diamond tool has a drawback that all of the abrasive grains are not bonded to the base metal with sufficiently large bonding strength, due to the random arrangement of the abrasive grains in the abrasive layer, so that some of the abrasive grains which are not firmly bonded to the base metal are removed from the base metal and accordingly stay on the polishing pad. The workpiece is scratched or damaged by the abrasive grains thus staying on the polishing pad.
The dresser disclosed in JP-A-10-71559, in which abrasive grains are not used, requires a process of forming the multiplicity of protrusions in its base metal and also a process of forming the diamond thin film by the vapor phase synthetic method, thereby resulting in a considerably increased manufacturing cost. Dressers disclosed in JP-A-10-44023 and JP-A-10-138120 are costly to manufacture, too.
In the method disclosed in JP-A-10-193266, in which the paste including the abrasive grains and the vitrified bond therein is applied onto the support body through the screen, the abrasive grains are unlikely to be sufficiently dispersed in the paste, due to possible sedimentation of the abrasive grains, where each of the abrasive grains has a diameter larger than 40 xcexcm. Thus, the paste applied onto the support body could be fixed to the support body in the sintering step, with agglomeration of the abrasive grains.
It is therefore a first object of the present invention to provide a vitrified bond tool having a construction which minimizes removal of the abrasive grains from the support body and accordingly prevents contamination or damage of a polishing tool and a workpiece to be polished by the polishing tool, and which is inexpensive to manufacture.
A second object of the invention is to provide a method suitable for manufacturing such a vitrified bond tool.
The first object indicated above may be achieved according to a first aspect of this invention, which provides a vitrified bond tool comprising: (a) a support body; (b) a vitrified bond layer which is formed on a working surface of the support body; and (c) a plurality of abrasive grains which are held by the vitrified bond layer so as to be fixed relative to the working surface of the support body and which are spaced apart from each other with spacing between adjacent ones of the abrasive grains.
In the vitrified bond tool according to the first aspect of the invention, the abrasive grains bonded to the vitrified bond tool are positioned relative to each other so as to be spaced apart from each other, so that each of the abrasive grains is bonded at an increased area of a surface thereof to the vitrified bond layer. Thus, all of the abrasive grains are bonded to the vitrified bond layer with sufficiently large bonding strength, thereby preventing removal of the abrasive grains from the vitrified bond layer or the support body, when this vitrified bond tool is used as a polishing or grinding tool for polishing or grinding a workpiece, or as a dressing tool for dressing a polishing or grinding tool. The workpiece polished or ground by this vitrified bond tool, or the polishing or grinding tool dressed by this vitrified bond tool and a workpiece polished or ground by the polishing or grinding tool is advantageously prevented from being contaminated and damaged by removal of the abrasive grains. The vitrified bond tool maintains its cutting sharpness throughout successive polishing or grinding operations, and accordingly exhibits an excellent polishing or grinding performance with high stability. In view of these advantages, the vitrified bond tool of this invention is suitable for dressing a polishing pad which is required to assure a high degree of flatness in a surface of a semiconductor wafer by polishing a considerably small amount of the surface of the wafer.
The vitrified bond tool provides other advantages. For example, the support body constituting a part of the vitrified bond tool may consist of a conventional support body. That is, a conventional support body can be used as the support body of the present vitrified bond tool, without necessity of a particular machining to the conventional support body.
In the present vitrified bond tool, agglomeration of the abrasive grains is prevented, so that each of the abrasive grains sufficiently exhibits its own polishing or grinding capacity. This makes it possible to reduce the amount or number of the abrasive grains to be used for each vitrified bond tool of the invention, thereby leading to a reduced manufacturing cost.
In the present vitrified bond tool in which each of the abrasive grains is bonded at an increased area of its surface to the vitrified bond layer, all of the abrasive grains are bonded to the vitrified bond layer with sufficiently large bonding strength, even with a reduced thickness of the vitrified bond layer. The reduced thickness of the vitrified bond layer facilitates protrusions of the abrasive grains from the vitrified bond layer after a firing step, i.e., after the manufacture of the tool, so that the vitrified bond tool does not have to be subjected to a truing operation, prior to an initial use thereof. That is, the vitrified bond tool exhibits an expected polishing or grinding performance even in the initial use without the truing operation.
The support body of the vitrified bond tool of the invention may be made of a ceramic or glassy material such as a silicon nitride or an alumina, without including any metallic material. Also in this view, the vitrified bond tool of the invention is suitable for dressing the polishing pad used to perform CMP operation for a semiconductor wafer which should be free from a metallic contamination.
It is desirable that thermal expansion coefficients of the abrasive grains, the vitrified bond layer and the support body are substantially equal to each other. That is, the difference between the abrasive grains and the vitrified bond layer in thermal expansion coefficients and the difference between the support body and the vitrified bond layer in thermal expansion coefficients are preferably not larger than 5xc3x9710xe2x88x926, more preferably not larger than 4xc3x9710xe2x88x926, and still more preferably not larger than 3xc3x9710xe2x88x926, for preventing cracking of the tool in the firing step.
According to a first preferred form of the first aspect of the invention, the abrasive grains protrude from a surface of the vitrified bond layer such that a distance over which each one of the abrasive grains protrudes from the surface of the vitrified bond layer corresponds to 20-70% of a diameter of the abrasive grain. This construction permits the abrasive grains to be held by the vitrified bond layer with a sufficiently high bonding strength, thereby preventing removal of the abrasive grains from the vitrified bond layer or the support body. If the protruding distance of each abrasive grain is larger than 70% of the diameter of the abrasive grain, the abrasive grain cannot be held by the vitrified bond layer with a sufficiently high bonding strength. If the protruding distance of each abrasive grain is smaller than 20% of the diameter of the abrasive grain, the dressing capacity of the vitrified bond tool is reduced.
According to a second preferred form of the first aspect of the invention, the abrasive grains are positioned relative to each other so as to be dotted on the working surface of the support body.
According to a third preferred form of the first aspect of the invention, the abrasive grains are positioned relative to each other such that the spacing between the adjacent ones of the abrasive grains is held in a predetermined range.
According to a fourth preferred form of the first aspect of the invention, the abrasive grains are positioned relative to each other by a precursor of the vitrified bond layer. It is noted that the precursor of the vitrified bond layer may be interpreted to correspond to a pattern layer which is described below.
The vitrified bond tools of the second, third and fourth preferred forms of the invention provide the same advantages as those of the vitrified bond tool of the first aspect of the invention as described above, and some additional advantages which will be clarified by description of preferred embodiments and examples as described below.
According to a fifth preferred form of the first aspect of the invention, the vitrified bond tool is designed as a dressing tool to be brought in sliding contact with a polishing surface of a polishing pad, for eliminating clogging in the polishing surface. The vitrified bond tool of this fifth preferred form further comprises, in addition to the plurality of abrasive grains as a plurality of first abrasive grains, a plurality of second abrasive grains whose average diameter is smaller than an average diameter of the first abrasive grains; wherein the working surface of the support body is a dressing surface which is forced onto the polishing surface of the polishing pad and which constitutes a part of a surface layer of the support body, at least the surface layer of the support body being made of an inorganic material; and wherein the second abrasive grains are held by the vitrified bond layer and are disposed on the dressing surface of the support body, such that the second abrasive grains are mingled together with each other, and such that the second abrasive grains are positioned between the first abrasive grains and are spaced apart from the first abrasive grains.
According to this fifth preferred form, in the dressing surface of the support body in which at least the surface layer is made of an inorganic material, the first abrasive grains which are spaced apart from each other are held by the vitrified bond layer, i.e., an inorganic bond layer, while the second abrasive grains whose average diameter is smaller than the average diameter of the first abrasive grains are also held by the vitrified bond layer such that the second abrasive grains are mingled together with each other. This construction prevents elution or effluence of a metallic component, even if a strong-acid fluid is used as the polishing fluid, thereby eliminating a risk of contamination of the workpiece. Further, the presence of the second abrasive grains between the adjacent ones of the first abrasive grains prevent the vitrified bond layer from being brought in contact with the polishing pad, thereby avoiding breakage of the vitrified bond layer.
The support body of the vitrified bond tool of this fifth preferred form may be made of a suitable ceramic material which has a high degree of chemical stability and sufficiently high degrees of strength and toughness for serving as a dressing tool. Such a ceramic material may be a sintered body of an inorganic material selected from alumina Al2O3, silicon nitride Si3N4, silicon carbide SiC, zirconia and mullite, or a glass having a high melting point. The vitrified bond layer of the vitrified bond tool of the fifth preferred form may be made of borosilicate glass, crystallized glass, silica glass, alumina, silicon nitride, silicon carbide, mullite, zirconia or other ceramic powders having sufficiently high degree of strength and toughness and a fusing point lower than that of the support body. Such suitable selections of materials for the support body and the vitrified bond layer are effective to avoid effluence of a metallic component into the polishing fluid thereby preventing the workpiece from being contaminated by an effluent metallic component, and also to avoid removal of the abrasive grains from the support body or the vitrified bond layer thereby preventing the workpiece from being scratched.
According to one advantageous arrangement of the fifth preferred form, the vitrified bond layer consists of a borosilicate glass including at least SiO2 and B2O3 such that the content of SiO2 therein is 40-70 wt % and the content of B2O3 therein is 10-30 wt %. The chemical composition of the borosilicate glass may include, for example, 40-70 wt % of SiO2, 0-20 wt % of Al2O3, 10-30 wt % of B2O3, 0-10 wt % of at least one kind of metal oxide RO which is selected from alkaline earth metals, and 0-10 wt % of at least one kind of metallic oxide R2O which is selected from alkaline metals. This arrangement makes it possible to burn or fire the vitrified bond layer at a low temperature, thereby facilitating the manufacturing of the vitrified bond tool.
According to another advantageous arrangement of the fifth preferred form, the first abrasive grains have a higher degree of hardness than the second abrasive grains. The first and second abrasive grains may be made of diamond, CBN, alumina, silicon carbide, silicon nitride, mullite, silicon dioxide (SiO2) or other material. For example, the first abrasive grains may be diamond abrasive grains having grain size of #100/#120, while the second abrasive grains may be alumina abrasive grains having grain size of #150/#180. According to this arrangement, the first abrasive grains which serve to dress the polishing pad have a comparatively high degree of hardness, while the second abrasive grains which serve to prevent contact of the vitrified bond layer with the polishing pad have a comparatively low degree of hardness and are made of a material comparatively cheap, thereby reducing the manufacturing cost of the vitrified bond tool.
According to still another advantageous arrangement of the fifth preferred form, the ratio of the number of the second abrasive grains to the number of the first abrasive grains is 1-10, or more preferably 2-5. This arrangement is effective to increase a load applied to each one of the first abrasive grains, thereby providing an excellent dressing performance. If the above-described ratio is lower than 1 or 2, namely, if the number of the first abrasive grains relative to the number of the second abrasive grains is too increased, the load applied to each first abrasive grain is made too small, resulting in a reduced dressing performance. On the other hand, if the above-described ratio is higher than 5 or 10, namely, if the number of the first abrasive grains relative to the number of the second abrasive grains is too reduced, the load applied to each first abrasive grain is made too large, undesirably increasing possibility of removal of the abrasive grains.
The above-indicated second object may be achieved according to a second aspect of this invention, which provides a method of manufacturing the vitrified bond tool as defined in the above-described first aspect of this invention. The present method comprises the steps of: (i) forming a pattern layer which includes a vitrified bond, in a predetermined pattern on the working surface of the support body; (ii) sprinkling the abrasive grains over the pattern layer before the pattern layer is dried; and (iii) firing the pattern layer and the abrasive grains which adhere to the pattern layer and are arranged in the predetermined pattern on the working surface of the support body.
The vitrified bond tool of the present invention can be manufactured according to this method of the second aspect of the invention with high efficiency and at a reduced cost. The present method provides the vitrified bond tool in which the abrasive grains are arranged in a direction parallel to the working surface of the support body so that the abrasive grains constitute a single layer, and in which a lower portion of each abrasive grain is embedded in the vitrified bond layer while an upper portion of each abrasive grain is not covered by the vitrified bond layer and protrudes from the vitrified bond layer. Further, the present method makes it possible to arrange the abrasive grains on the support body in various patterns. By suitably arranging the abrasive grains on the support body depending upon its purpose, it is possible to manufacture the vitrified bond tool having the abrasive-grains-holding capacity and the polishing capacity suitable for the purpose.
The present inventors proposed, in JP-A-10-193266, the vitrified bond tool characterized by including the support body, and the abrasive grains cooperating with each other to form an abrasive layer which is bonded by the vitrified bond to the support body. The present inventors have now accomplished the present invention, as a result of a further study, which provides the vitrified bond tool wherein the positions of the abrasive grains relative to the working surface of the support body are more exactly controllable two-dimensionally or three-dimensionally.
According to a first preferred form of the second aspect of the invention, the method further comprises the steps of: (iv) forming a backing layer which includes a vitrified bond, on the working surface of the support body; and (v) forming a pattern layer which includes a vitrified bond, in a predetermined pattern on the backing layer.
According to a second preferred form of the second aspect of the invention, the method further comprises the step of (vi) applying one of a paste and a slurry including a vitrified bond, on the working surface of the support body, for thereby forming a coating layer which surrounds each of the abrasive grains on the working surface of the support body.
The vitrified bond tool defined above in the fifth preferred form of the first aspect of the invention can be manufactured according to a method comprising the steps of: (vii) mixing the first and second abrasive grains with each other with a predetermined ratio of the number of the second abrasive grains to the number of the first abrasive grains; (viii) printing an abrasive-grains-adhering paste on the dressing surface, such that the pattern layer is formed of the abrasive-grains-adhering paste, on the dressing surface, in a dotted pattern consisting of a plurality of dots each having a diameter which is smaller than an average diameter of the first abrasive grains and which is larger than 30% of the average diameter of the first abrasive grains; (ix) sprinkling the first and second abrasive grains over the pattern layer formed on the dressing surface, so that ones of the first and second abrasive grains adhere to the pattern layer; (x) removing the others of the first and second abrasive grains which are not bonded to the pattern layer; and (xi) firing the pattern layer and the above-described ones of the first and second abrasive grains, so that the above-described ones of the first and second abrasive grains are held by the vitrified bond layer, so as to be fixed relative to the dressing surface of the support body.
According to the present method, the mixture of the first and second abrasive grains are sprinkled over the pattern layer which is formed on the dressing surface, in the dotted pattern consisting of the plurality of dots each having the diameter which is smaller than the average diameter of the first abrasive grains and which is larger than 30% of the average diameter of the first abrasive grains, so that ones of the first and second abrasive grains adhere to the pattern layer. The others of the first and second abrasive grains which do not adhere to the pattern layer are removed, and then the pattern layer and the adhering ones of the first and second abrasive grains are fired in the firing step, so that the adhering ones of the first and second abrasive grains are held by the vitrified bond layer, so as to be fixed relative to the dressing surface of the support body.
In the vitrified bond tool manufactured according to the present method, the first abrasive grains are held by the vitrified bond layer so as to be fixed relative to the dressing surface and are spaced apart from each other, while the second abrasive grains are held by the vitrified bond layer so as to be fixed relative to the dressing surface and are mingled together with each other such that the second abrasive grains are positioned between the first abrasive grains and are spaced apart from the first abrasive grains. Since at least the surface layer which is partially constituted by the dressing surface is made of the inorganic material, there is no risk of effluence of a metallic component even if a strong-acid fluid is used as the polishing fluid. Since the second abrasive grains whose average diameter is smaller than the average diameter of the first abrasive grains are positioned to be spaced apart from each other or to be spaced apart from the first abrasive grains, each of the second abrasive grains is bonded at an increased area of a surface thereof to the vitrified bond layer with a sufficiently large bonding strength. Further, the presence of the second abrasive grains between the first abrasive grains on the vitrified bond layer prevent the vitrified bond layer from being brought in contact with the polishing pad, thereby avoiding breakage of the vitrified bond layer.
The abrasive-grains-adhering paste may be, preferably, a slurry liquid having a high degree of viscosity, and includes an inorganic-bonding-agent powder which is dispersed in an organic solvent, water or other solvent, and further includes, as needed, a dispersing agent serving to restrain agglomeration of the inorganic-bonding-agent powder, a thickener serving to increase the viscosity of the abrasive-grains-adhering paste for facilitating the printing of the paste on the dressing surface, and a caking agent serving to bond the inorganic-bonding-agent powder to the substrate when the abrasive-grains-adhering paste is dried. It is noted that the dispersing agent, thickener and caking agent are dissipated at the firing step.
Preferably, the present method may further include the step of applying an inorganic-bonding-agent paste on the entirety of the dressing surface of the support body, before the abrasive-grains-adhering paste is printed. In this inorganic-bonding-agent applying step, the inorganic-bonding-agent paste is applied onto the dressing surface of the support body with a sufficiently large amount thereof which permits the first abrasive grains to be bonded to the support body with a sufficiently large bonding strength. Thus, the abrasive-grains-adhering paste is printed with a thickness thereof not so large as where this inorganic-bonding-agent applying step is not implemented, namely, where the first and second abrasive grains have to be fixed to the support body by only the abrasive-grains-adhering paste. In other words, where this inorganic-bonding-agent applying step is implemented before the abrasive-grains-adhering paste is printed, the thickness of the abrasive-grains-adhering paste no longer has to be so large, as long as the thickness of the printed abrasive-grains-adhering paste is sufficiently large for permitting the first and second abrasive grains to merely adhere to the abrasive-grains-adhering paste. Therefore, the operation for printing the abrasive-grains-adhering paste is facilitated without a risk of dripping of the dots of the dotted pattern of the abrasive-grains-adhering paste, which dripping would be caused where the thickness of the printed abrasive-grains-adhering paste is very large.
The dots of the pattern layer are arranged on the dressing surface, preferably, with a density of the dots being constant over the entirety of the dressing surface such that the number of the dots per unit area is constant over the entirety of the dressing surface. This arrangement is effective to substantially equalize loads applied to the respective first abrasive grains, to each other, thereby increasing the polishing efficiency and preventing removal of the first abrasive grains.
Each of the dots preferably has a diameter corresponding to 30-70% of the average diameter of the first abrasive grains, so that each one of the first abrasive grains adheres to the corresponding one of the dots when the abrasive grains are sprinkled over the pattern layer formed on the dressing surface.